This invention pertains to improved catalytic hydrogenation of heavy hydrocarbonaceous feedstocks utilizing catalytic multi-stage ebullated bed reactors for producing desired lower boiling hydrocarbon liquid products. It pertains particularly to such catalytic multi-stage hydrogenation processes having increased catalyst loading and liquid volume together with reduced gas hold-up in each reactor, and thereby provides improved performance efficiency for the processes.
In conventional catalytic hydrogenation processes for heavy hydrocarbon feedstocks utilizing multi-stage ebullated bed reactors, the hydrogen gas recycle rate in each reactor is usually kept relatively high to assure that excess hydrogen gas exists in the catalyst bed to provide the necessary chemical hydrogenation reactions with the feedstock. However, such excess hydrogen flow requires relatively high superficial gas velocities in the reactor(s), which results in less available volume for the reacting liquid and increased gas hold-up in the reactor. Because the feedstock hydrogenation and hydrocracking reactions occur predominantly in the liquid phase, this conventional practice has the result of undesirably reducing the percentage of feedstock liquid being exposed to and reacted with the catalyst in the reactor, and undesirably reduces process performance. Also, for known catalytic ebullated bed type reactors which utilize internal gas/liquid separation devices, the volume of catalyst in a particular size reactor is undesirably limited.
Many prior art patents have been directed to various improvements in catalytic hydrogenation processes for heavy hydrocarbon feedstocks utilizing catalytic ebullated bed reactors, and have disclosed various operational parameters for such reactors. For example, U.S. Pat. No. 3,183,180 to Schuman et al, U.S. Pat. Nos. 4,217,206 and 4,427,535 to Nongbri et al disclose hydrogenation of petroleum residua using catalytic single stage ebullated bed reactors having internal gas/liquid separation, and U.S. Pat. No. 4,576,710 to Nongbri et al and U.S. Pat. No. 4,853,111 to MacArthur et al disclose use of such catalytic two-stage reactors. Other prior art patents have disclosed hydrogenation process improvements utilizing catalysts having various compositions and pore structures, and specific reaction conditions based on characteristics of the feedstocks. However, a need still remains for providing a comprehensive improved catalytic multi-stage ebullated bed reactor system which is capable of producing improved hydrogenation process performance efficiencies.